1. Technical Field
The present invention relates to a video projector using a 2-D spatial light modulation element, such as a liquid crystal panel and a DMD.
2. Background Art
FIG. 7 is a view schematically showing the configuration of a laser display in the related art described in detail, for example, in Non-Patent Document 1. Light beams from laser light sources 100a through c for three colors, RGB, are combined by dichroic mirrors 102a and 102b, and scanned in the horizontal direction (X-direction) by a polygon scanner 104 and in the vertical direction (Y-direction) by a galvanometer scanner 105 to be irradiated onto a screen 108. In this instance, a video is displayed on the screen 108 by modulating intensity by light modulators 106a through 106c according to an input video signal. For example, in order to display a moving image corresponding to an NTSC video signal, about 500 scan lines in the horizontal direction are displayed for 30 frames per second, and the number of horizontal scan lines in total is 15,000 per second. This can be achieved by rotating the polygon scanner 104 having 30 faces at 30,000 rpm. The galvanometer mirror 105 is oscillated to reciprocate in the vertical direction 30 times per second. The resolution in the horizontal direction is determined by a modulation rate of the light modulators with respect to the scan rate. For example, in order to obtain the resolution comparable to 500 TV lines in the horizontal direction at the scan rate specified above, a bandwidth of about 10 MHz is necessary on the basis of 500×15,000=7,500,000. Such a bandwidth can be achieved with a light modulator using the acousto-optic effect or a light modulator using the electro-optic effect.
The display configured in this manner is characterized in that it can display a sharp image having high color purity by using laser light sources having adequate wavelengths because light beams from the respective light sources for RGB are monochromatic light. Sharp color display of each monochromatic light can be achieved, for example, by using a krypton ion laser having a wavelength of 647.1 nm as the red light source, a helium-cadmium laser having a wavelength of 441.6 nm as the blue light source, and a second harmonic of a neodymium-doped YAG laser having a wavelength of 532 nm as the green light source.
The configuration of FIG. 7, however, has a problem that the need to rotate the polygon scanner 104 having 30 faces at 30,000 rpm as described above increases the device in size and also increases noises. In addition, when an incident beam on the polygon scanner 104 is positioned on a boundary line of reflection surfaces, the reflected beam is split into two directions, which makes it impossible to display a video. An image can be therefore displayed only when an incident beam goes incident on any one of the reflection surfaces to fit within. In order to obtain sufficient efficiency for utilization of light, the reflection surfaces of the polygon scanner 104 need to be sufficiently large in comparison with the diameter of the incident beam. Hence, even when the number of reflection surfaces of the polygon scanner 104 is increased, a specific area has to be secured. This increases the polygon scanner 104 in size.
Non-Patent Document 1: Baker et al., “A large screen real-time display technique”, Proc. Society for Information Display 6th Nati'l Symp., 85-101 (1965)